1. Field of the Invention
The present invention relates to a method and system for constraining, protecting, insulating, and inserting orthopedic implants.
2. Description of the Related Art
Fusion of bones in orthopedics often involves metallic implants being attached to bones to fixate them together during the healing process. In certain small hone procedures, such as the fusion of toe or finger bones, it is difficult to use metallic implants that attach to the cortex of the bone because there is limited bone surface area. In these procedures, it is often desirable to use intramedullary implants that insert into the medullary canal of two adjacent bones and thus fixate them to each other. Implants made from shape memory materials, such as nitinol, are particularly suited for this approach because they can be inserted into the two bones, expand upon warming by the body, and thus fixate bones to one another.
However, the process of constraining, protecting, insulating, inserting, and positioning such an implant during the surgical procedure is difficult. Some existing shape memory implants are simply held by a pair of forceps, exposed to air, and are thus susceptible to premature shape change from operating room temperatures. Premature shape change renders the implant useless.
It also can be difficult to insert and impact a small intramedullary implant into hard bone without damaging the implant. Striking the implant with a mallet can deform the implant or damage its biocompatible surface finish. Similarly, intramedullary implants for use in larger bones are also difficult to constrain, insulate, and/or insert.
Orthopedic implants also may be shaped to conform to anatomy. For example, an intramedullary implant for use in toe fusions might feature an angle such that when the toe heals it is angled downward in a normal anatomic position. An implant of this type, with a bend or curve, is more difficult to hold and insert because subjecting the implant to a linear impacting force that passes through a bend might cause the implant to be deformed or damaged.
An intramedullary implant is also difficult to position properly. If it is placed into one bone first, for example, it can then be dislodged and moved out of position by the process of inserting into a second bone.
Other companies have commercialized plastic storage blocks for shape memory implants. These blocks serve the sole purpose of constraining the implant in a deformed state. For example, BioMedical Enterprises, Inc., Memometal, Inc., Biopro, Inc., and Core Essence Orthopedics all sell shape memory implants that are stored in plastic blocks. The blocks constrain the implant, but do not insulate the shape-changing portion of the implants, cannot be impacted, do not protect the implant during the insertion process, and do not assist in positioning the implant in the proper anatomic orientation. In U.S. Pat. No. 4,665,906, Jervis refers to a method for restraining a shape memory device, however, no images of such a device are provided. In U.S. Publication 2009/0018556, Prandi describes a surgical instrument that manipulates a shape memory implant for insertion into bone. This device does not allow for impacting the implant into position, does not protect the implant from metal-on-metal surface marring, and does not insulate the implant in any way.
Accordingly, a method and apparatus for constraining, protecting, insulating, inserting, and positioning an orthopedic implant is desirable. The apparatus can be made to accommodate any shape of implant to permit simple insertion.